As compared with traditional scanning optical systems having a rotary polygonal mirror (polygon mirror), recently proposed resonance type optical deflecting devices have advantageous features that the optical deflecting device can be made quite small in size; slow power consumption; and theoretically no surface tilt of the mirror surface.
On the other hand, in the resonance type optical deflecting devices since, in principle, the deflecting angle (displacement angle) of the mirror changes sinusoidally, the angular speed is not constant. U.S. Pat. No. 4,859,846 and U.S. Patent Application, Publication No. 2006/152785 have proposed a method for correcting this.
In U.S. Pat. No. 4,859,846, a resonance type deflector having oscillation modes of a fundamental frequency and a frequency threefold the fundamental frequency is used to accomplish triangular-wave drive. FIG. 35 shows a micromirror that accomplishes approximately triangular-wave drive. Here, the optical deflecting device 12 comprises oscillators 14 and 16, torsion springs 18 and 20, driving systems 23 and 50, detecting systems 15 and 32, and a control circuit 30. This micromirror has a fundamental resonance frequency and a resonance frequency approximately threefold the fundamental resonance frequency, and it is driven at a combined frequency of the fundamental frequency and the threefold frequency. As a result of this, the oscillator 14 having a mirror surface is driven in accordance with triangular-wave drive, whereby optical deflection having an angular speed of deflection angle less changing as compared with sinusoidal drive is accomplished. Here, the detecting systems 15 and 32 detect oscillation of the oscillator 14, and the control circuit 30 produces a driving signal necessary for accomplishing the triangular-wave drive. The micromirror is then driven through the driving systems 23 and 50.